1. Field of the Invention
The present invention relates to a thermally enhanced electronic package, and more particularly, to an electronic package with high thermal dissipation capability.
2. Description of the Related Art
Continued demand for improved performance of semiconductor products results in greater operating frequencies and greater power consumption. Therefore, electrical packages having high thermal conductivity capable of effective heat dissipation to reduce the interconnect junction temperature are needed for such products. One example is a type of semiconductor device called a liquid crystal display (LCD) driver.
A typical LCD driver package is illustrated in FIG. 1. The LCD driver package 10 comprises a driver chip 11 and a tape carrier 14. The tape carrier 14 includes a polyimide (PI) substrate 143, a wiring layer (or copper foil) 142 formed on the substrate 143, and a resistant (solder mask) 141 overlaying the wiring layer 142. The driver chip 11 is mounted on the tape carrier 14 by flip-chip bonding. The bumps 13 formed on the active surface of the driver chip 11 are connected to the wiring layer 142 of the tape carrier 14. An insulator (or resin) 12 is filled in the gap between the driver chip 11 and a tape carrier 14 to protect the bumps 13 and the inner leads of the wiring layer 142.
Larger LCD television panel size and higher operating refresh rate demand high power/high density LCD drivers. Therefore, a heat sink is needed to lower the temperature of the LCD driver in a chip on film (COF) package, preferably below 70□. Accordingly, FIGS. 2A to 2E show several typical LCD driver packages equipped with heat sinks.
As shown in FIG. 2A, the LCD driver package 20 comprises a driver chip 11 and a film carrier 24. The film carrier 24 includes a PI substrate 243, a wiring layer 242 formed on the substrate 243, and a resistant 241 overlaying the wiring layer 242. A first heat sink 251 is attached to the passive surface of the driver chip 11, and a second heat sink 252 is adhered to the substrate 243 by a thermal adhesive 26. To improve the thermal dissipation, conductive columns 244 connect the wiring layer 242 and the adhesive 26 through the substrate 243.
By contrast, the second heat sink 252 of the LCD driver package 20′ is directly attached to the substrate 243, as shown in FIG. 2B. Compared with the configuration shown in FIG. 2A, the LCD driver package 2a in FIG. 2C also has two heat sinks (251, 252), but the second heat sink 252 is not underneath the driver chip 11. The layout of the wiring layer 242′ of the film carrier 24′ is different from that of the film carrier 24. The second heat sink 252 is adhered to the substrate 243 by the adhesive 26.
The LCD driver package 2b in FIG. 2D has only the second heat sink 252 which is directly attached to the substrate 243. The second heat sink 252′ of the LCD driver package 2c in FIG. 2E is underneath the driver chip 11, and has an opening 253 aligned with the driver chip 11.
Considering the aforesaid conventional LCD driver packages, a common thermal dissipation method is to use a thermally conductive adhesive loaded with high percentage (by weight) of fillers to attach a sheet of aluminum film as a heat sink to the film side of the COF package. However, as an exposed surface of the aluminum heat sink needs to be further electrically insulated, an additional organic polymer film 37 with low thermal conductivity such as a polyimide film is repeatedly adhered on a surface of the second heat sink 252 of the COF (chip on film) package 30, as shown in FIG. 3. The organic polymer film 37 is attached to the second heat sink 252 by an additional adhesive 36.
The multilayer configuration makes the thermal management of the package very inefficient. In addition, the conventional thermal conductive adhesive depends on direct physical contact of filler particles for heat conducting. This requires high filler loading to ensure good contact between particles which makes the heat transfer very inefficient and sensitive to the surrounding temperature. Moreover, using aforesaid aluminum film as a heat sink, the bending capability of COF packages will become limited. Therefore, to remedy the conventional drawbacks, novel materials and methods are needed to improve the thermal performance of the package.